# Ligatures in figures and pdftex

In the following example, the 'ff' ligature in the figure labels (in 'differential') disappears when pdflatex is used, but the fault does not occur if latex-dvips-ps2pdf is used instead. Both lualatex and xelatex produce the correct results, using the pdf version of the figure. Is there a problem with the figure, or is this a bug in pdftex?

\documentclass{article}
\usepackage{graphicx}
\begin{document}
\includegraphics[width=0.9\textwidth]{Cluster2}
\end{document}

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Try \pdfinclusioncopyfonts=1
\pdfinclusioncopyfonts (integer)
If positive, this parameter forces pdfTEX to include fonts from a pdf file loaded with \pdfximage, even if those fonts are available on disk. Bigger files might be created, but included pdf files are sure to be embedded with the adequate fonts; indeed, the fonts on disk might be different from the embedded ones, and glyphs might be missing.